A conventional active type optical distance measuring sensor is known as a device configured to irradiate light from a light source for projection of light such as an LED (Light Emitting Diode) toward an object, to detect reflected light from the object with a photodetecting element, and thereby to output a signal according to the distance to the object. For example, a PSD (Position Sensitive Detector) is known as an optical distance measuring sensor of an optical triangulation type capable of readily measuring the distance to the object. In recent years, however, there are expectations for development of an optical distance measuring sensor of an optical TOF (Time-Of-Flight) type, in order to achieve more accurate distance measurement.
There are demands for an image sensor capable of simultaneously acquiring distance information and image information by a single chip, for example, in on-vehicle use, use in automatic manufacture systems in factories, and so on. There are also expectations for an image sensor capable of acquiring a range image consisting of a single piece of distance information or multiple pieces of distance information, separately from the image information. It is preferable to apply the TOF method to such a distance measuring sensor.
For example, a solid-state imaging device described in Patent Literature 1 is known as a range image sensor based on the foregoing TOF method. In the range image sensor described in Patent Literature 1, each of pixels arrayed in a two-dimensional pattern is composed of a rectangular charge generating region, transfer gate electrodes provided respectively along a pair of two opposed sides of the charge generating region, floating drain regions for accumulating respective signal charges transferred by the transfer gate electrodes, discharge gate electrodes provided respectively along a different pair of two opposed sides of the charge generating region and configured to discharge background light charges from the charge generating region, and discharge drain regions for accepting respective background light charges discharged by the discharge gate electrodes. This range image sensor calculates the distance to the object, based on quantities of charges distributed into the floating drain regions. Since the background light charges generated in the charge generating region are discharged, influence of background light is reduced, so as to increase the dynamic range.